Phase equilibria in the system CaF sub 2 -AlF sub 3 -Na sub 3 AlF sub 6 and part of the system CaF sub 2 -AlF sub 3 -Na sub 3 AlF sub 6 -Al sub 2 O sub 3

• Published in: Journal of the American Ceramic Society 1980-01, Vol.63 (5-6), p.254-261
• Main Authors: Craig, Douglas F, Brown, Jesse J
• Format: Article
• Language: English
• ISSN: 0002-7820

The complete phase-equilibrium diagram of the system CaF sub 2 -AlF sub 3 -Na sub 3 AlF sub 6 and the subsolidus portion of the system CaF sub 2 -AlF sub 3 -Na sub 3 AlF sub 6 -Al sub 2 O sub 3 were established from microscopic, powder XRD, quench, and DTA data obtained from samples encapsulated in sealed tubes and either reacted in the solid state or melted and recrystallized. The system Na sub 3 AlF sub 6 -CaF sub 2 contains a simple eutectic with no compound formation or solid solution. The system CaF sub 2 -AlF sub 3 -Na sub 3 AlF sub 6 contains 2 ternary compounds, NaCaAlF sub 6 and NaCaAl sub 2 F sub 9, which melt incongruently at 735 and 712 Degrees C, resp.; NaCaAlF sub 6 exists in 3 polymorphic forms with transitions at 610 and 722 Degrees; NaCaAl sub 2 F sub 9 is bcc with a sub 0=10.765 Angstroms. The 3 binary and 2 ternary compounds divide the system into 8 compatibility triangles. Along the NaCaAlF sub 6 -Na sub 3 AlF sub 6 join, 7 mol% NaCaAlF sub 6 is soluble in Alpha-cryolite at 525 Degrees and 42% in Beta-cryolite at 731 Degrees. The quaternary system Na sub 3 AlF sub 6 -AlF sub 3 -CaF sub 2 -Al sub 2 O sub 3 contains 8 compatibility tetrahedra.